The invention relates to storage racks for storing nuclear fuel assemblies both during transport and during stationary storage. Preferably, the racks are highly overdamped, enabling them to best withstand vibrations caused by seismic events or rough handling.
Fuel for nuclear reactors is typically configured in the form of elongated fuel rods, which may be separate, stand-alone elements, or may be positioned within canisters. Hereinafter, the fuel rods and rod/canister combinations are referred to as fuel assemblies. Both before and following use, the fuel assemblies must be stored and/or transported with great care. To assure that such care is achieved, storage racks are often used to support a plurality of fuel assemblies in a generally parallel, spaced-apart configuration, while maintaining the fuel assemblies in a subcritical array environment. During storage, the racks and the fuel assemblies contained therein, may be completely submerged in a pool of water. The water provides cooling and additional shielding from nuclear radiation.
The fuel storage racks of the prior art typically consist of an assembly of hollow cells, each defined by an array of elongated rectangular cross-section boxes or compartments. The boxes are typically made by forming sheets of stainless steel into elongated rectangular cross-section tubes and welding the corners of the elongated tubes together to form a matrix of elongated hollow cells, each adapted the receive a single fuel assembly. Exemplary storage racks are disclosed in U.S. Pat. Nos. 4,695,424, 4,857,263, 4,948,553, and 4,366,115. A neutron absorbing (or "poison") material, such as borated stainless steel, is typically welded or otherwise rigidly affixed to each of the walls of boxes to absorb neutron flux from the fuel assemblies which may be positioned within the boxes, thereby avoiding an undesirable concentration of neutrons.
These prior art storage racks suffer from several disadvantages. For example, neutron absorbing elements, and particularly those made borated stainless steel, are expensive and difficult to form and weld to the walls of the boxes. Further, the individual cells are known to be weak along the top edge and have little torsional or crush strength. In addition, storage racks constructed in this way have little resistance to vibration, such as may be caused by seismic events. Due to the reactive nature of the nuclear fuel assemblies, such damage to the storage racks can be disastrous.
Accordingly, it is an object of the present invention to provide an improved storage and/or transport rack for nuclear fuel assemblies.
Another object of the present invention is to provide an improved storage rack for nuclear fuel assemblies which is highly overdamped to enable the rack to withstand the vibration of seismic events or rough handling such as may be encountered during transportation of the rack.
It is another object to provide a storage rack for nuclear fuel assemblies which has improved torsional and crush strength.
A further object is to provide an improved storage rack for nuclear fuel assemblies which may De easily and inexpensively manufactured.
Other objects of the invention will in part be obvious and will in part appear hereinafter.